Such a process and such an apparatus are described in WO 89/11021. In the known process two glass plates, which have been assembled to form an insulating glass pane, are temporarily provided with an access opening to the interior space between the glass plates in that one of the glass plates is resiliently flexed before or after the assembling of the glass plates. To that end the known apparatus is provided with vacuum cups, which are arranged in a vertical striplike recess in a wall and are adapted to be extended as far as to the forward surface of the wall and to be retracted parallel to themselves so as to be disposed some millimeters behind the forward surface of the wall. The wall itself is provided with holes, which are regularly distributed over the surface of the wall and through which air can also be sucked, to retain and position the glass plate on the wall. The glass plate which is gripped on both sides because air is sucked through the holes in the wall is caused to bulge in a strip-like area by the action of the suction cups in the striplike recess in the wall and high flexural stresses are thus produced in the glass because the sense of curvature is reversed several times in the flexing range. Owing to the high flexural stress it is difficult to flex thick glass plates and any microcracks existing in the glass plate may cause the glass plate to break whereas such cracks would not become apparent unless the glass plate was flexed. In accordance with WO 89/11021 the stresses can locally be alleviated in that the wall has a curved surface in a region which adjoins the recess on both sides so that there is a gradual transition from the planar portion of the wall into its recess and the steepness of the curvature at the edge of the recess can be decreased although the sense of curvature of the glass plate is still reversed several times.
In the prior art it has also already been proposed to flex the glass plate along one of its edges. But it has not been stated what apparatus is to be used for that purpose.